Effects of multilure components on twig-crotch feeding by European elm bark beetles.

The three components of the European elm bark beetle pheromone dispensed from polyethylene vials attached to the boles of healthy juvenile elms affected the rates of beetles landing and twig feeding on the baited trees. Maximum attraction to the tree occurred when all three pheromone components were presented together in a ratio of 1∶1∶8 for 4-methyl-3-heptanol (H), α-multistriatin (M), and α-cubebene (C). M released either alone or in excess of its natural ratio with H and C induced twig-crotch feeding. H presented alone had no effect on attraction or twig-crotch feeding, but in combination with M it induced landing on and boring into the tree bole. We concluded that the ratio of M and H being released influenced incoming beetles either to land on and colonize the bole or to feed in twig crotches. M in excess of H, known to occur when most females are mated, terminates colonization and deflects incoming beetles to crowns of elms.